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In Our Field: Trangenic cotton: Safe and effective pest control

June 14, 2001|By ERIC T. NATWICK, Entomology adviser, University of California-Imperial County Cooperative Extension

Imperial County's cotton acreage has doubled from 2000 to 2001 and nearly all cotton planted is transgenic cotton.

Transgenic cotton varieties have been genetically engineered to carry a gene from the bacteria Bacillus thuringiensis (Bt) or to have resistance to certain herbicides.

Bt products have been available for use on various crops for many years to control lepidopteran pests (caterpillars, loopers, worms). After many years of development the first transgenic cotton varieties with Bt genes and their lethal protein toxin were available to control worm pests in California for planting in 1996. Since 1997, approximately 80 percent of the cotton in Imperial County was planted to Bt cotton.

Transgenic Bt cotton varieties will help in the management of many cotton pests such as beet armyworm, western yellowstriped armyworm, alfalfa looper, cabbage looper, cotton bollworm, tobacco budworm, cotton leafperferator, saltmarsh caterpillar and pink bollworm.

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Not all worm pests are controlled equally by Bt cotton. The single gene Bt cotton currently available has been shown to be less efficacious on beet armyworm and cotton bollworm than for many other worms attacking cotton.

Under heavy population pressure from cotton bollworm or beet armyworm, non-Bt insecticides may need to be applied to control these pests. Bt cottons should not be considered a replacement for good pest management practices such as monitoring fields for pest problems, cultural practices such as short season cotton, and occasional use of insecticides.

Bt protein toxin in transgenic cotton varieties will not control many cotton pests such as flea beetles, mites, aphids, whitefly, lygus bugs, cotton fleahoppers, leafhoppers, boll weevils, and stink bugs.

Cotton fields should still be monitored for pink bollworm adults even though their presence will be less of an indicator of a potential control problem.

Pheromone traps should be used to monitor the general area-wide moth flight trends during the season and boll cracking should continue as the primary means of detecting pink bollworm infestations. Bt cotton varieties will not kill every larva, so monitoring must continue.

Finding pink bollworm first or second instar larvae or their damage such as warts or frass will not be unusual and should not trigger a treatment as these worms should not continue to feed and will die. Therefore, do not be alarmed unless cutting or cracking bolls reveals larger (third or fourth instar) larvae.

How do transgenic cotton varieties help our economy and the environment? When growers use Bt cotton varieties there are some great advantages: 1) fewer insecticide applications and lower bills, 2) beneficial insects can become more abundant in cotton fields to help control insect pests, 3) there is less worry about sudden worm pest outbreaks and 4) there are potentially higher lint and seed yields due to fewer pest problems and insecticide sprays.

Local growers also benefit from herbicide-resistant transgenic cotton varieties.

Herbicide-resistant cotton can help hold down growing costs by lowering fuel and man hour costs needed for cultivation and by reducing herbicide costs.

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